1. Technical Field
The present invention relates to precision aspirators, suited for use in automated liquid sample analyzers, for taking up liquid from containers by suction. In particular the invention relates to precision aspirators employing liquid suction tubes that can pierce caps sealing the mouths of containers holding diagnostic samples and reagents, and that can discriminate among such containers.
2. Description of Related Art
Automated liquid sample analyzers, for example, blood-sample analyzing machines, employ an aspirating pipette to take up a predetermined amount, or aliquot, of sample liquid such as blood plasma sequentially from a row of tubular sample containers. The sample containers are held in a sample rack that is transferred in container-by-container increments into an aspirating position beneath the pipette. Each container is paused in the aspirating position, in which a mechanism manipulating the pipette brings it down into the container, actuates suction through the pipette to take up an aliquot, brings the pipette back up, and shifts it to an ejecting position. In the ejecting position, the aliquot is ejected into, for example, a reaction vessel containing reagents for a blood-analyzing test.
Some of the containers loaded into the sample rack may be sealed, with a rubber cap for example, or otherwise stoppered. The tips of the needle-type aspirating pipettes used for taking up aliquots from sample containers are cut obliquely to pierce a sealed or stoppered container.
An aspirating tube having an aspiration aperture formed on its circumferential surface apart from the tip, so that when the aspirating tube penetrates a rubber cap, rubber debris does not clog the aspirating tube, as Japanese Laid-Open Pat. App. No. 9-304400 discloses, is known.
On the other hand, Japanese Pat. No. 2511549, corresponding to U.S. Pat. No. 5,201,232, discloses a liquid sampling device having a sampling probe for withdrawing sample liquids from open containers, as well as a sampling needle for closed containers. Therefore, the liquid sampling device is operable to suit either type of containers--capped (closed) containers, or uncapped (open) containers. Furthermore, the disclosed liquid sampling device distinguishes open containers from closed containers using a detector that reads an identification label or card provided on the container exterior.
Nevertheless, the device as taught in Japanese Pat. No. 2511549, in order to identify the containers from which it withdraws samples, requires special labels or cards affixed to the containers, as well as a detector to read them. Consequently, if the labels or cards are affixed improperly, the device cannot identify containers correctly. In addition, equipping the device with two kinds of aspirators makes the mechanism large and complex.
If for example a single aspirating tube is to be used for both open and closed containers, some situations make it desirable to provide the aspiration aperture in the tip of the aspirating tube. For instance, the desire to improve quantitating accuracy in micro-samples of a few .mu.l, to decrease sample-liquid dead volume (the quantity that cannot be aspirated and remains in the container), or to decrease the amount of aspirating tube immersed into a sample liquid in order to prevent inter-contamination of the liquids necessitates that the aspiration aperture be in the tip of the aspirating tube. However, if the aspiration aperture is provided in the tip of the aspirating tube, the tube is likely to get clogged when it penetrates the cap of a closed container.
In conventional liquid sampling devices, the aspirating tube is shifted vertically to take up an aliquot, which operation requires relatively little force to bring the pipette down into an open container, yet considerably greater force to stab the pipette through a sealed container. Supplying large force for an open container leads to mechanical losses, hampers agility and, leads to operational problems such as damage to the aspirating tube by its being crushed on the bottom of the container due to the container's vertical position. For example, to shift horizontally the liquid aspirating tube and its large drive source if integrated into one unit confronts the practical problems that the unit cannot travel horizontally at high speed due to its large size and weight, and that the horizontal shifting mechanism then also must be large.